A surge arrester is used to limit dangerous or undesired overvoltages in electrical lines and devices. Surge arresters render it possible to avoid lines and devices becoming damaged as a result of an overvoltage.
Gas-filled surge arresters, which are also described as gas discharge tubes, are surge arresters by which the overvoltage is reduced as a result of a gas discharge self-arcing in the gas discharge tube. The surge arresters function according to the gas-physical principle of the arc discharge, wherein once the arrester response voltage is achieved, in short referred to as a response voltage or as an ignition voltage, an arc is formed within nano seconds in the gas-tight discharge chamber. The overvoltage is effectively short-circuited as a result of the ability of the arc to conduct a high current. Conventional gas discharge tubes generally have response voltages of 70V up to a few kilo volts which limits their range of use. Gas-filled surge arresters that have a maximum 10 kV response voltage have been hitherto available.
In order to protect medium voltage transformers in the effective voltage range of 3 kVrms to 36 kVrms (the suffix “rms” at the end of the unit subsequently describes a root mean square) from overvoltages that can occur by way of example during a lightning strike, it is possible to use surge arresters that comprise a series connection of metal oxide varistors and an air spark gap, as is described by way of example in CA 2027288. The disadvantage of the open air spark gap is that the response voltage is dependent upon the environmental conditions. In order to reduce this effect, the air spark gap must be protected by suitable measures and hitherto this has not been achieved satisfactorily.